Circuit breaker



G. E. JANssoN Nov. 10, 1936.

CIRCUIT REAKER Filed May` l Nov. 10, 1936. G. E. JvANssoN 2,060,758

- I CIRCUIT BREAKER Filed May l, 1953 2 Sheets-Sheetl 2 llllllllll! Z 79 7, m t" aa Patented Nov. 10, 1936 `*UNITED STATES PATENT CFFICE CIRCUIT BREAKER Application May 1, 1933, Serial No. 668,724

20 Claims.

This invention relates in general to circuit interrupters having pressure chambers with variable discharge openings, and more particularly to circuit interrupters in which the variable discharge openings are arranged so as to cause a blast of arc extinguishing fluid to iiow into the arc drawn within the pressure chamber.

In the pressure chamber circuit interrupters of the prior art it has been recognized that when the throat through which a movable contact passes is made large enough to permit a sufciently rapid discharge of fluid upon interruption of large currents to prevent excessive pressure rise, difficulty will be had in interrupting l5 currents of small magnitude because the throat opening is so large that the velocity of fluid discharged through the throat will be insui'icient to successfully extinguish the arc. Various schemes have been proposed to obviate this difliculty by providing the explosion chamber with valve controlled discharge openings independent of the throat opening through which the movable contact passes, however these independent Openings do not discharge arc extinguishing fluid into the arc stream, moreover, when tubular movable contacts are used it is possible that the fluid will ilow through the tubular contact with insuflicient velocity to extinguish the arc when the current is small.

An object of the invention is to provide a circuit interrupter ofthe pressure chamber type with a passageway for thei'low of arc extinguishing fluid into the arc stream, and provide means for varying the cross-sectional area of said passageway in accordance with the pressure generated by the arc.

Another object of the invention is to provide a circuit breaker of the pressure pot type with means for causing a blast of arc extinguishing fluid to discharge into the arc stream, and provide means for preventing said discharge of fluid until the pressure within the pot builds up to a predetermined value.

A further object of the invention is to provide a circuit breaker of the pressure pot type with a single discharge path across the arc stream and through a tubular movable Contact, and provide a pressure responsive valve mechanism associated with the movable Contact for maintaining substantially constant pressure within said pot during circuit interruption by controlling the flow of fluid through the tubular contact.

A further object of the invention is to provide a circuit interrupter of the pressure pot type in 'E which the pot and a contact therein are movable to break contact with a xed contact and thereby draw an arc within the movable pot.

A still further object of the invention is to provide a circuit interrupter of the pressure pot l-type with an auxiliary pressure pot within the main pressure pot and surrounding the movable contact rod, the auxiliary pot being resiliently carried by the movable contact and so arranged that the discharge from the auxiliary pot is controlled in accordance with the pressure generated 5 within the pot.

An additional object of the invention is to provide improved details of construction of a circuit interrupter of the pressure pot type various novel features of which will be apparent from l0 the description and drawings herein, and will be more particularly pointed out in the claims.

y Various illustrative embodiments of this invention are shown in the accompanying drawings in which: l5

Fig. 1 is a vertical section view of a circuit breaker pressure pot mechanism embodying the present invention;

' Fig. 2 is a vertical section view of a modied form of a circuit breaker pressure pot mecha- 20 nism;`

Fig. 3 is a vertical section View showing how the features of Figs. 1 and 2 may be applied to a pressure pot circuit breaker of the liquid immersed type; 2.5

Fig. 4 is a vertical section view of a modication of Fig. 3 illustrating an additional application of the present invention;

Fig. 5 is a vertical section view of a diiierent form of liquid immersed pressure pot circuit 30 breaker embodying the present invention;

Fig. 6 is a vertical section view similar to Fig. 5 showing the contacts slightly separated during initial circuit interruption;

Fig. 7 is a vertical section view similar to Fig. 35v

5 showing the contacts further separated during circuit interruption; and

Fig. 8 is a sectional view of a modified form of pressure pot structure.

Referring now tov Fig. 1, an outer pressure pot l0` is shown as comprising a casing member I I, preferably of metal, and a throat member I5, preferably of insulating material, provided with a contact passageway therethrough. Casing member II is preferably detachably mounted on an ring 22 of insulating material be arranged to 55 'Y cover the exposed surfaces thereof.

A body of arc extinguishing fluid 23 is contained within the inner pressure pot and the level thereof is rendered visible by means of level indicator 24 which may be provided with a filler cap 60 CII 25. Fluid 23 is preferably an aqueous solution rendered slightly conductive by the addition of chemicals, however it is to be understood that any of the well known aro extinguishing liquids, such as oil, may be used. A drain plug 25 in casing Il may be removed to drain liquid which may collect in the outer casing.

The inner pressure pot is provided with a xed contact 2l which cooperates with a tubular movable contact 28 noting that the movable contact is guided by guide member 29 and may be operated by any well known mechanism (not shown). Throat member I3 closely surrounds tubular contact 28 so that the leakage therebetween is minimized. The electric circut to be broken will be connected to movable contact 28 and a suitable terminal, such as member 38. Tubular contact 28 is provided with means for controlling the discharge of fluid therethrough comprising a piston valve member 3l slidable inside contact 28 which is provided with ports 32 and 33. Valve member 3l is biased to a closed position by means of a spring 34 which acts upon abutment 38 which is held in xed relation relative to contact 28 by means of adjusting rod 35 and a block 3l which is secured to contact tube 28.

Regarding the operation of Fig. 1, when tubular contact 28 is moved upwardly to interrupt currents of small magnitude, a pressure generating arc will be established between the lower portion thereof and fixed contact 2T. However, there will be no discharge exit for the pressure thus generated until the pressure increases to a predetermined value as determined by the calibration of spring 34. Upon upward movement of valve member 3l, port 32 will first be uncovered thereby establishing a discharge passageway into the outer pressure pot. The gas and liquid discharged through this opening will be forced into hollow contact 28 and will thus flow transversely through the arc thus exerting a strong extinguishing action. A portion of the arc will thus be drawn into the hollow contact tube 28 as more clearly shown in Fig. 3 and inasmuch as the electrostatic field within contact tube 28 is substantially zero, the tendency for the arc to reignite after the current passes through zero is minimized. If the pressure within the inner pressure pot further increases, valve member 3I will be raised further against spring 34 to open port 33, and it is thus seen that the above described valve mechanism provides means for controlling the cross-sectional area of the discharge passageway in accordance with the pressure generated. When larger currents are to be interrupted, the valve member 3l will open the discharge ports sooner than with smaller currents and it is thus seen that the valve mechanism will operate to maintain an eflicient and substantially constant pressure within the inner pressure pot for large currents as well as for small currents. The distance through which valve member 3l must travel before port 32 is opened may be adjusted by turning threaded rod member 35 in block 31.

Fig. 2 is substantially the same structurally as Fig. 1 except that the outer pressure pot is provided with an insulating liner 38 and a plurality of cooling plates 39 are held in spaced relation between throat members I3 and I5 by means of insulating spacers 4l and insulating rods 42. It is to be noted that plates 39 have apertures therethrough in alinement with the contact passageways in throat members l5 and I9 and that these plates are preferably of conical or dished shape so that the arc extinguishing liquid condensed thereon may flow back into the inner pressure pot. The valve mechanism within tubular contact rod 28 is slightly different structurally from that described in connection with Fig. 1, noting that a rod 44, having adjusting nuts 45 thereon, is slidable through block 3l and is securely fastened to piston valve 43. Valve member 43 is hollow and is preferably made of light weight metal in order to reduce the inertia thereof. Rod 44 carries a pressure adjusting block 48 which may be secured to shaft 44 in various positions in order to adjust the compression of spring 34 which is interposed between blocks 3l and 46.

The operation of Fig. 2 is substantially the same as described in connection with Fig. l, except that the vaporized liquid discharged from ports 32 and 33 is condensed by cooling plates 39 which are so arranged that the major portion of the liquid discharged from the inner pressure pot is condensed and returned thereto. It is to be noted that the length of travel of valve member 43 before port 32 is uncovered may be adjusted by means of adjusting nuts 45 and that the pressure at which valve member 43 begins to move may be adjusted by means of adjusting member 46. In some instances, it is desirable that spacer members 4l be in the form of annular rings substantially completely enclosing the space between throat members l5 and I8, however, it is prefered that these spacer members be so spaced circumferentially that a plurality of annular discharge passageways are thereby formed leading into the main pressure pot.

Although circuit interruption is accomplished in Figs. 1 and 2 by moving contact member 28 upwardly, it is to be understood that these pressure pots can be inverted and immersed in an insulating liquid so that circuit interruption is accomplished by a. downward movement of contact member 28 in a manner well known in the art, noting for example Fig. 3.

In Fig. 3 a pressure pot, such as disclosed in connection with Figs. l and 2, is shown attached to a conventional insulating bushing 48 by means of a supporting member 4l. The pressure pot is immersed in any well known arc extinguishing liquid 48, such as oil, which is contained in a tank 5|. It is to be understood that two such devices as shown in Fig. 3 will be utilized to interrupt the circuit in two places, the tubular contact members 28 being carried by a bridging member 52 which is operated by any suitable switch operating mechanism (not shown). The valve mechanism shown in connection with Fig. 3 is substantially the same as shown in Fig. 2 except that compression adjusting block 46 has been omitted for the sake of clearness. Upon downward movement of bridging member 52, an arc will be drawn between xed contact 27 and tubular contact 28, and when the pressure within the pot increases to a predetermined value valve member 43 will move downwardly relative to contact tube 28 thereby successively opening ports 32 and 33 to establish a discharge passageway into the liquid 49 surrounding the pressure pot. Throat member i9 closely surrounds contact tube 28 so that liquid and gas discharged across the arc and through the tubular contact iiows substantially solely through the tubular contact, noting however that if the arc is not extinguished before contact tube 2B is withdrawn from throat member I9 a secondary blast of arc extinguishing uid will then ow through throat member 9 into the path of the arc and exert a further are extinguishing action. Throat member I9 closely surrounds contact tube 28, noting that the pressure pot will refill with arc extinguishing fluid after contact tube 28 has been moved to its final circuit opening position in which contact tube 28 is completely withdrawn from throat member I9.

Fig. 4 shows a modied form of pressure pot circuit breaker within the scope of the invention. A supporting member 41 is bolted to insulating bushing 48. An insulating shell member 53 and a plurality of baffle partitions 54 and 55 spaced by insulating rings 56, 51 and 58 are held in place vby means of a bottom plate 59 which is biased toward plate 41 by means of bolts 62 which aresurrounded by insulating sleeves 63. The heads of bolts 62 are insulated from possible contact with conductive gases by means of a protective plate 64 of insulating material which is secured to plate 59 by means of bolts 65 of insulating material. An insulating throat bushing 6I is secured to bottom plate 59 and closely surrounds contact tube 1I so that the leakage therebetween is minimized. A xed contact 66 is detachably mounted in supporting spider 61 which in turn is resiliently mounted on supporting member 41 by means of springs 68 and bolts 69. Current is conducted from spider member 61 to plate member 41 by means of one or more pig-tail conductors 1|J.

A movable tubular contact 1| is secured to a bridging member 52 and is provided with a removable contact portion 12. The bottom portion of tubular contact 1l is provided with a valve member 13 which is biased to its closed position by means of spring 14 which is carried by a spring support 15. Tubular contact 1I is also provided with one or more discharge openings 16 which are adapted to be placed in communication with the interior of the pressure pot when the pressure therein exceeds a predetermined value.

Regarding the operation of Fig. 4, after a predetermined downward movement of bridging member 52, a pressure generating arc will be established between contacts 61 and 12. Inasmuch as throat bushing 6| closely surrounds tubular contact 1|, there will be substantially no discharge from the pressure pot until the pressure therein builds up to a sufficient Value to move valve 13 downward. Upon opening of port 16 arc extinguishing liquid will ow from the interior of the pressure pot, across the arc and intothe hollow contact 1I and thence through port 16 to the exterior of the pot. For small currents valve 13 may not open until contact 12 has moved downwardly a substantial distance, whereas for large currents the valve 13 will open much sooner thereby tending to maintain substantially constant pressure within the pressure pot by regulating the cross-sectional area of the discharge passageway in accordance with the pressure within the pot.

Referring now to Figs. 5, 6 and 7, a main pressure pot comprises a top plate member 11, preferably of metal, whichis supported from an insulating bushing (not shown) by means of a bolt 18. The main pressure pot also comprises an insulating tube 19 suitably secured toy plate member 11 and a bottom plate 8l, preferably of insulating material, suitably secured to insulating tube 19. Insulating tube 19 is provided with a plurality of vent openings 88. Plate member 11 carries a xed contact 82 which cooperates with a movable contact 83 which is flxedly supported `,from bridging member 85 by means of spring cage 84 for example. ridging member 85 is moved to its open and closed positions by means of an'operating rod 86 with a resilient connection therebetween comprising springs 81.

An auxiliary pressure pot member 88, having a stop member 9| secured thereto, slidably surrounds movable contact 83 and is biased upwardly by means of spring 92 which is carried in spring cage 84. The auxiliary pressure pot defines a pressure chamber 89 which surrounds the movable contact 83 near its upper end. A plurality of raised portions 98 on the upper end of pot member 88 define a plurality of narrow discharge openings between member 88 and contact 82. Cage member 84 is provided with relief openings 93 which permits pressure pot member 88 to move downwardly relative to cage 84 without excessive dash pot action.

Regarding the operati-on of Figs. 5, 6 and '1, Fig. shows the circuit breaker in its normal closed position with pressure pot member 83 biased against contact 82 by means of spring 92. Referring to Fig. 5, upon initial downward movement of operating rod 86 and before it arrives at the position shown in Fig. 6, contact rod 83 will disengage from stationary contact 82 and establish a pressure generating arc within the arc ex tinguishing fluid maintained in pressure chamber 89. The vaporization of fluid within chamber 89 will generate a pressure therein and thereby cause arc extinguishing fluid to discharge through the arc and through the narrow discharge spaces between member 88 and stationary contact 82. The pressure within these narrow discharge openings by reason of the velocity of the discharge therethrough, and by reason of the fact that the pressure within the main pressure pot is greater than outside thereof, will cause member 88 to move downwardly against the compression of spring 92 if the pressure is sufficiently high, thereby controlling the pressure within chamber 89 by regulating the cross-sectional area of these discharge passageways.

Fig. 6 shows the circuit breaker in a partly opened position with auxiliary pressure pot mem ber 88 moved downwardly against the pressure of spring 92 by reason of the pressure action between stationary contact 82 and the top face of member 88. As bridging member 85 moves farther down, a portion thereof will move into engagement with stop member 9| thereby causing pressure pot member 88 to move downwardly therewith.

If the arc is not extinguished by the discharge from the auxiliary pressure pot, a secondary blast from the main pressure pot into the liquid surrounding the main pressure pot will occur when the bridging member 85 has moved to the position shown in Fig. '1. Vented openings 88 in the main pressure pot will prevent the pressure therein from rising to an unsafe value.

Fig. 8 shows a modiiied form of main pressure pots suitable for use in connection with Figs. 5, 6 and '1. This pressure pot comprises in general an insulating ring 94 adjacent plate member 11 forming a relatively large pressure chamber. A plurality of thin annular plates of insulating material are spaced by means of insulating washers 96 which are circumferentially spaced, noting that bolts 91 are used to hold the assembly together. The spaces between the insulating plates define a plurality of annular discharge passages which are effective to rapidly cool the gases discharged from the auxiliary pressure pot and also serve to aord quick relief passageways also if the auxiliary pressure pot has withdrawn from the main pressure pot. It is to be understood that the main pressure pot may in some instances be omitted, inasmuch as the pressure regulating feature of the invention is present Whether a main pressure pot be used or not.

Although but a few embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

l. A circuit interrupter ycomprising a pressure chamber containing an arc extinguishing fiuid, a fixed contact within said pressure chamber, a movable contact wlthdrawable from said pressure chamber and cooperable with said fixed contact to establish a pressure generating arc, means defining a passage providing for the flow of arc extinguishing fluid through said arc and out of said pressure chamber, and means for varying the cross-sectional area of said passage in accordance with the pressure generated by said arc.

2. A circuit interrupter comprising a pressure chamber containing an arc extinguishing fluid, a xed contact within said pressure chamber, a movable contact withdrawable from said pressure chamber and cooperable with said iiXed contact to establish a pressure generating arc, means providing for the flow of arc extinguishing fluid through said arc and out of said pressure chamber, and means for regulating the ow of the fluid discharged from said chamber in accordance with the pressure generated by said arc so that the velocity of the fiuid discharged into said arc is maintained substantially constant for small currents as well as for large currents.

3. A current interrupter comprising a pressure pot containing an larc extinguishing fluid and having a Contact passageway therein, a contact structure within said pot, a tubular contact movable through said passageway to connect and disconnect with said Contact structure, said tubular contact having substantially the same cross-sectional dimensions as said passageway so that the pressure generated by the arc drawn between said contacts upon disconnection thereof causes a blast of arc extinguishing fluid to flow across said arc and out of said pot through said tubular contact before said tubular contact moves out of said passageway, and means in said tubular contact responsive to the forces produced by said arc current for regulating the flow of arc extinguishing uid through said tubular contact.

4. A current interrupter comprising a pressure pot containing an arc extinguishing fluid and having a contact passageway therein, a contact structure within said pot, a tubular contact movable through said passageway to connect and disconnect with said contact structure, said tubular contact having substantially the same cross-sectional dimensions as said passageway so that the pressure generated by the arc drawn between said contacts upon disconnection thereof causes a blast of arc extinguishing fluid to iiow across said arc and out of said pot through said tubular contact before said tubular contact moves out of said passageway, and pressure responsive means for preventing the flow of said arc extinguishing iiuid through said tubular contact until the pressure within said pot exceeds a predetermined value.

5. A circuit interrupter comprising a pressure pot containing an arc extinguishing fluid and having a single opening therein, a Contact member mounted within said pot, a tubular contact slidable through said opening into engagement with said first mentioned contact, said tubular contact being of such cross-sectional size as to substantially fill said opening and being Withdrawable through said opening to establish a pressure gener-ating arc within said pot, said tubular contact affording the sole discharge exit for arc extinguishing fluid under pressure during the withdrawal movement of said tubular Contact through said opening, and pressure responsive means within said tubular contact for preventing the discharge of fluid through said tubular contact until the pressure within said pot builds up to a predetermined value.

6. A circuit interrupter comprising a pressure chamber containing an arc extinguishing fluid and having a discharge passageway therethrough, a contact mounted within said chamber, a movable hollow contact arranged to move through said passageway, so as to engage and disengage with said first mentioned Contact, and means cooperating mechanically with said hollow contact for controlling the flow of extinguishing fluid through said movable hollow contact.

7. A circuit interrupter comprising a pressure `pot containing an arc extinguishing fluid and having a passageway therethrough, a contact mounted within said pot, a movable hollow contact arranged to move through said passageway to make and break contact with said rst mentioned contact, and means carried by said hollow contact for controlling the ovv of arc extinguishing fluid through said hollow contact.

8. A circuit interrupter comprising a pressure pot containing an arc extinguishing fluid and having a discharge passageway therethrough, a contact mounted Within said pot, a movable contact rod arranged to move through said passageway to make and break contact with said rst mentioned contact, said movable contact having a passageway therethrough for the ow of arc extinguishing fluid therethrough to the exterior of said explosion pot upon the generation of pressure within said explosion pot caused by an arc between said contacts, and valve means including said passageway of said movable contact responsive to the pressure within said explosion pot for regulating the flow of arc extinguishing fluid through the passageway in said movable contact.

9. A circuit interrupter comprising a pressure pot, a second pressure pot mounted within said first mentioned pressure pot and containing a vaporizable arc extinguishing liquid, said pressure pots having alined passageways therethrough for a movable contact, a contact mounted within said second pot, a movable contact arranged for withdrawal through said passageways to initially establish an arc in said second pressure pot, said movable contact having an axial hole therethrough for the discharge of arc extinguishing liquid from said second explosion pot, and means in the path of discharge of said liquid for regulating the flow of said iiuid.

l0. A circuit interrupter comprising a pressure pot, a second pressure pot mounted within said rst mentioned pressure pot, and containing an arc extinguishing fluid, said pressure pots each having an opening therein for the passage of a 75.

movable contact, a butt contact mounted within said second pressure pot, a tubular contact movable through said openings to m-ake and break circuit with said butt contact, said tubular Contact being arranged to conduct the fluid caused to flow therethrough to the exterior of said pot by reason of the pressure generated within said pot by an arc between said contacts upon separation thereof, and a spring biased valve arranged in the path of travel of the fluid in said tubular contact for maintaining a substantially uniform pressure within said pot.

11. A circuit interrupter comprising a pressure pot containing an aqueous arc extinguishing liquid, a contact mounted within said pressure pot,

a larger pressure pot surrounding said first mentioned pressure pot, said pressure pots each having a contact passageway therethrough in alinement with said contact, a plurality of cooling plates mounted within said larger pressure pot in spaced relation between said passageways, said' plates having apertures therethrough in alinement with said passageways, and movable contact means operable to cause liquid vaporized by the arc drawn upon withdrawal movement thereof to discharge into said cooling plates.

12. A circuit interrupter comprising a pressure pot containing an aqueous arc extinguishing liquid, a Contact mounted within said pressure pot, a larger pressure pot surrounding said first mentioned pressure pot, said pressure pots each having a contact passageway therethrough in alinement with said contact, a plurality of cooling plates mounted within said larger pressure pot in spaced relation between said passageways, said plates having apertures therethrough in alinement with said passageways, and movable contact mechanism withdrawable through said passageways to establish a pressure generating arc, said mechanism comprising means for causing said liquid to discharge between said cooling plates only after the pressure generated by said arc exceeds a predetermined value.

13. A circuit interrupter comprising a pressure pot containing an arc extinguishing fluid and having a contact passageway therethrough, a fixed contact mounted within said pressure pot in alinement with said contact passageway, and reciprocable mechanism comprising a movable contact member operable to engage and disengage with said xed contact, said reciprocable mechanism also comprising an auxiliary pressure pot surrounding said movable contact member and movable therewith and in spaced relation to said fixed contact so as to form therewith a passageway between said pressure pot and said auxiliary pressure pot.

14. A circuit interrupter comprising a pressure pot containing an arc extinguishing fluid and having a contact passageway therethrough, a xed contact mounted within said pressure pot in alinement with said contact passageway, a contact member, and means for withdrawing said contact member through said passageway from engagement with said fixed contact to establish a pressure generating arc, a tubular member slidable on said contact member, means for biasing said tubular member toward said fixed contact so that said tubular member remains in engagement with said xed contact after said contact member disengages with said xed contact and spacing means between said tubular member and said fixed contact.

15. A circuit interrupter comprising a pressure pot containing an arc extinguishing fluid and having a contact passageway therethrough, a xed contact mounted within said pressure pot in alinement with said contact passageway, a contact member, means for withdrawing said contact member through said passageway from engagement with said fixed contact to establish a pressure generating arc, a tubular member slidably surrounding said contact member so as to form an auxiliary pressure pot within which said arc is established, and means responsive to the pressure generated within said auxiliary pressure pot for controlling the discharge of arc extinguishing fluid therefrom.

16. A circuit interrupter comprising a fixed contact immersed in an are extinguishing fluid, a movable contact, means for causing said movable contact to engage and disengage with said xed contact, a member slidably surrounding said movable contact, and resilient means arranged to bias said slidable member into engagement with said fixed contact when said movable contact engages said fixed contact so as to denne a substantially closed pressure pot having a discharge passageway, said resilient means being operable to control the cross-sectional area of said discharge passageway in accordance with the pressure generated within said pressure pot during disengagement of said movable contact with said fixed contact.

17. A circuit interrupter comprising a pressure chamber containing an arc extinguishing fluid, a pair of current carrying contact members separable within said chamber to establish a pressure generating arc, one of said contact members being completely withdrawable from said pressure chamber, means for causing the fluid discharged from said chamber to flow into and through said arc so as to extinguish said arc, and means for maintaining the velocity of said fluid discharged into and through said arc at a substantially constant value, said means being operable'to regulate the flow of fluid discharged from said pressure chamber in accordance with the pressure within said chamber.

18. A circuit interrupter comprising a pressure pot containing an arc extinguishing uid, a hollow contact, a second contact, means whereby said contacts are relatively movable and cooperable to make and break contact in said fluid, and means cooperating mechanically with said hollow contact for controlling the flow of uid through said hollow contact.

19. A circuit interrupter comprising a pressure pot containing an arc extinguishing fluid, a hollow contact, a second contact, means whereby said contacts are relatively movable and cooperable to make and break contact in said fluid, and means carried by said hollow contact for regulating the flow of fluid through said hollow contact in accordance with the current through said contacts.

20. A circuit interrupter comprising a pressure pot containing an arc extinguishing fluid, a hollow contact, a second contact, means whereby said contacts are relatively movable and cooperable to make and break contact in said fluid to draw a pressure generating arc, and means cooperating mechanically with said hollow contact for controlling the flow of fluid through said hollow contact in accordance with the pressure generated by said arc.

GUSTAV E. JANSSON. 

